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GCSE Chemistry > C4 - Chemical Calculations > Flashcards

C4 - Chemical Calculations Flashcards

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1
Q

What is a pro of having balanced symbol equations?

A

You can work out the masses of the reactants and the products.
Number of moles of substances used in a reaction

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2
Q

What numbers do you NEVER change when balancing equations?

A

The subscripts (small ones)

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3
Q

What is the equation for number of moles?

A

Moles = mass (g)/ relative formula mass

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4
Q

Relative formula masses are compared by measuring them relative to…

A

Atoms of carbon which has an aromic mass of 12.

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5
Q

What actually is 1 mole of a substance?

A

This is its relative formula mass in moles.

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6
Q

What is the exact value of avogrados constant?

A

6.02 x 10^23

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7
Q

What is a mole?

A

This is an atoms or a substances relative fornula mass in grams.

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8
Q

Which is the limiting reactant?

A

This is the reactant which gets used up first.

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9
Q

How can you find the ratio of number of moles of substances in a chemical reaction? To find out what is the limiting factor

A

Dividing the mass you have of each substance by its relative formula mass, giving you no. Of moles of each substance. Then by putting this into a ratio you can see which substance will be the limiting reaction by balancing the equation.

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10
Q

Calculation for percentage yield?

A

Percentage yield = (actual mass of product produced/ maximum theoretucal mass of product possible) x 100

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11
Q

What are some factors effecting percentage yield?

A

Some of the reactants may be lost in handling/left in the apparatus,
The reactants may not be pure
Some of the desired product may be lost during its seperation from the reaction mixture
Reactants may give unwanted products

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12
Q

Is it possible to have a 100% reactant yield?

A

No this is not possible.

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13
Q

Why would a company want a reaction with a higher percentage yield?

A

It would cost the company less money to make more of the desired product.

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14
Q

What is the atom economy?

A

This is how many of the original atoms from the reactants end up in the desired product.

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15
Q

What is the calculation for atom economy?

A

Percentage atom economy = (relative formula mass of desired product/sum of the relative formula masse of the reactants) x 100 ( you use the big numbers to multiply the Mr, this is the only one where you use them )

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16
Q

How would you express atom economy?

A

As a percentage

17
Q

What is 1 decimetre^3 equal to?

A

1000 cm^3

18
Q

What is the unit chemists use for concentration?

A

g/dm^3

19
Q

What is the equation for concrentrations?

A

Amount of solute (g) / volume of solution (dm^3)

Or

(Amount of solute (g) / volume of solution (cm^3) ) x 100

20
Q

How can you increase the concentration of an aqueous solution?

A

Adding more of the solute

Evaporating off some of the water from the solution.

21
Q

What is a titration?

A

This is where you measure the exact amounts of an alkali and an acid needed to react and therefore nuetralise each other.

22
Q

How can you tell when the solution is nuetralised in a titration?

A

You can do this by using an acid/base indicator.

23
Q

How would you find the mass or moles of a substance used in a titration?

A

By simply rearraging the formula number of moles = mass (g)/ formula mass

24
Q

How do you work out the mass needed of a reactant needed for a chemical reaction?

A

Balance equation
Mark your ? and ✅
Find the number of mols for ✅ ( mass / Mr)
Use the equation to work out the ratio between ? and ✅ and find out what the mols of ? should be
Use mass = mols x Mr to find mass

25
Q

For more info on titration and method go to C4.7/8

A

It is very hard to explain on a flashcard!

26
Q

What is the volume of 1 mole of any gas at room temp?

A

24000 cm^3

27
Q

What is the equation to find the number of moles of gas?

A

No. Of moles = volume of gas (dm^3)/24 dm^3

28
Q

What is the actual temperature of room temperature in chemistry?

A

This is 20°C

GCSE Chemistry (15 decks)

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